Method and system using encoded periodic digital sum variation (DSV) as pilot signal and controlling tracking error using crosstalk from the pilot signal

ABSTRACT

A data conversion method from m bits of data words into n bits of code words in recording or transmission, in which n is larger than m. A number of bit &#34;0&#34; arranged between one bit &#34;1&#34; and a next bit &#34;1&#34; is restricted to at most 4 in a code string of each code word, and a pair of groups of the n bits of code words corresponding to CDSs (code word digital sum) of two codes +1 and -1 are allowed to correspond to the m bits of data words. One of the two codes +1 and -1 is selectively used according to a DSV (digital sum variation) control signal to convert the m bits of data word into the n bits of code word. A pilot signal formation method using the data conversion method for obtaining a tracking error signal in a magnetic recording and reproducing apparatus, and a rotary magnetic head device for use in a magnetic recording and reproducing apparatus are also disclosed.

This application is a divisional of application Ser. No. 08/120,857,filed on Aug. 31, 1993, which is now U.S. Pat. No. 5,365,232 issued onNov. 15, 1994, which is a continuation of Ser. No. 07/743,888, filed onAug. 12, 1991 and now abandoned, the entire contents of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

i) Field of the invention

The present invention relates to a data conversion method for convertingdigital data into suitable signals for a recording or transmissionsystem in recording or transmitting the digital data, a pilot signalformation method using the data conversion method for obtaining atracking error signal in a magnetic recording and reproducing apparatussuch as a digital VTR (video tape recorder) system or the like, and arotary magnetic head device for use in the magnetic recording andreproducing apparatus.

ii) Description of the related arts

A conventional data conversion system, for example, an 8/10 modulationsystem has been developed, as disclosed in "The Dat ConferenceStandard", June, 1987.

In the conventional 8/10 modulation data conversion system, digital datais delimited by data words of 8 bits, and the data words are convertedinto code words of 10 bits, as shown in FIGS. 1 to 3. In FIG. 1, a dataword a of 8 bits and a first table selection signal Q' of 1 bit areinput to an encoder 1, and the encoder 1 outputs a code word b of 10bits and a second table selection signal Q of 1 bit for a next codeword. A flip flop 2 receives the second table selection signal Q for thecode word b and delays the table selection signal Q for one data word a

In the encoder 1, for instance, a data conversion table shown in FIG. 2for converting the data words into code words is stored in a ROM (readonly memory) or the like. In the data conversion table, 256 data wordsof hexadecimal codes of "00" to "FF" correspond to code words of CDS(code word digital sum)=0 in one-to-one relation and also to the codewords of CDS≠0 with reference to a pair of CDS values of +2 and -2, andtables Q'=-1 and Q=+1 are composed of data words of CDS=+2 and CDS=-2,respectively. The signal Q selects the CDS (table) so as to suppressdivergence of charges in a code word string.

In FIG. 3, signals a, b and Q correspond to those at the points a, b andQ in FIG. 1, and a signal c is obtained after a NRZI (non-return-to-zeroinverse) modulation where inversion is carried out by data "1". A signald represents DSV (digital sum variation) at the end of each code wordafter the NRZI modulation.

The operation of the 8/10 modulation system described above will now bedescribed in detail.

First, when an 8 bit data word a of FF and a first table selectionsignal Q'=-1 are input to the encoder 1, the encoder 1 outputs a 10 bitcode word b of 1111101010 having a CDS=+2 corresponding to FF of thesignal Q'=-1 and a second table selection signal Q=-1. Then, the 10 bitsignal is converted from a parallel signal into a serial signal, and theNRZI modulation of the serial signal is carried out. Hence, the DSVvalue of the end of the code word becomes +2.

Then, when a data word a of 00 is input to the encoder 1, a 10 bit codeword b of 0101010101 having a CDS=0 corresponding to 00 of the signalQ'=-1 resulted from delaying the just preceding output signal Q=-1 byone symbol in the flip flop 2, and a signal Q=1. As a result, the DSVvalue of the end of the code word b after the NRZI modulation is +2.

Next, when a data word a of 11 is input to the encoder 1, a 10 bit codeword b having a CDS=-2 corresponding to 11 of the signal Q'=1 and asignal Q =-1. Accordingly, the DSV value of the end of the code word bafter the NRZI modulation is 0. That is, in general, when an 8 bit dataword a is input to the encoder 1, the encoder 1 outputs a code word bselected from either the table where Q'=-1 or Q'=1 corresponding to thedata word a according to a first table selection signal Q output rightbefore, and as a result, a DSV value at the end of each code word bafter the NRZI modulation is restricted to 0 or ±2 n. This means thatthe divergence of the DSV is suppressed, and as a result, a DC free dataconversion excluding any direct current component can be realized.

In the conventional data conversion system, as described above, sincethe CDS values of the code words obtained in the conversion are selectedfrom only 0 and ±2, the suppression control of the DSV values for thecode words can not be positively or actively carried out, and thespectrum of the code word includes relatively low frequency components.Further, when a DSV control circuit is provided to use a DSV value asone of data, the DSV value can not be controlled every code word.

In FIGS. 4 and 5, there is shown a pilot signal formation circuit and atracking error detecting circuit for use in producing a tracking errorin a conventional magnetic recording and reproducing apparatus, asdisclosed in Japanese patent laid-open No. Sho 59-68862. As shown inFIG. 4, a reference oscillator 101 for generating a reference signal, apresetable counter 102, a flip flop 103, a filter 104 and a mixer 105for adding a reference sine wave signal 106 output from the filter 104and a data signal 107 representing an audio or visual signals areconnected in series. A magnetic head 109 for carrying out the recordingor reproducing of a signal onto or from a magnetic medium 122, such as amagnetic tape, is coupled with the mixer 105 through a turnover switch108 for selecting recording or reproducing, and a frequency dividingratio controller circuit 10 receives a track switch signal 111 and arecord and reproduction switch signal 112 and controls the frequencydividing ratio of the presetable counter 102.

A low pass filter 113 for inputting a reproduction signal 114 fed fromthe magnetic head 109 via the turnover switch 108, a mixer 115 foradding the reproduction pilot signal output from the low pass filter 113and the reference signal 106 fed from the filter 104, an amplifier 116and a divider circuit 117 are connected in series. The divider circuit117 outputs a signal to a pair of envelope detector circuits 119a and119b through respective band pass filters 118a and 118b, and adifferential amplifier 120 receives the output signals of the twoenvelope detector circuits 119a and 119b and compares them to output atracking control signal 121. FIG. 5 illustrates the magnetic medium 122such as the magnetic tape and the magnetic head 109 which is movablealong recording tracks 123 on the magnetic tape in the conventionalmagnetic recording and reproducing apparatus.

The operation of the conventional magnetic recording and reproducingsystem shown in FIGS. 4 and 5 will now be described in detail.

First, in the recording of a signal onto a magnetic tape, the frequencydividing ratio of the presetable counter 102 is switched by thefrequency dividing ratio controller circuit 110 according to the trackswitch signal 111, and the output signal of the presetable counter 102is further frequency-divided by the flip flop 103. The filter 104receives the output signal of the flip flop 103 and outputs thereference sine wave signal (pilot signal) 106 to the mixer 105, and themixer 105 adds the reference signal 105 and the data signal 107 tooutput a recording signal to the magnetic head 109 via the turnoverswitch 108. The magnetic head 109 records the recording signal onto themagnetic tape 122.

In this case, since the track switch signal 111 is changed every timethe recording track is changed, for example, four kinds of pilot signalsf1, f2, f3 and f4 can be recorded onto the magnetic tape, as shown inFIG. 5. In this instance, it is necessary to determine the frequenciesof the pilot signals from, for instance, several tens of kHz to severalhundreds of kHz, so that the data signal 107 may not be damaged when thepilot signal is extracted and the data signal 107 is reproduced.

By determining the frequencies of the four pilot signals f1 to f4 to thefollowing formulas in consideration of a 4 frequency pilot system of an8 mm VTR (video tape recorder) for public use,

    f1+fA=f2, f2+fB=f3                                         (1)

    f4+fA=f3, f1+fB=f4                                         (2)

when the recording signal is reproduced from the magnetic tape by themagnetic head 109 shown in FIG. 4 in a reproducing mode, the pilotsignal mixed with the data signal 107 recorded onto the magnetic tape isalso reproduced. This pilot signal can be extracted by the low passfilter 113, and at this time, not only the pilot signal for the tracknow being scanned by the magnetic head 109 but also the pilot signals ofboth adjacent tracks thereto are picked up as crosstalk.

Since the frequency of the pilot signals of the adjacent tracks is lowenough compared with the video signal or the like, for example, even inan azimuth recording, the azimuth effect will be negligible, and thusthe pilot signals of the adjacent tracks can be reproduced as a largecrosstalk amount. When the pilot frequency of the reference signal 106written in the scanning track is added to the pilot signals reproducedas above in the mixer 115, a beat is caused between the reference signal106 and the pilot signals due to the crosstalk of the adjacent tracks,and beat frequencies of the beat signals fA and fB in formula (1)above-described can be obtained.

As shown in FIG. 5, for instance, on reproducing the track 123 in whichthe pilot signal having the frequency f2 is written, the pilot signalshaving the frequencies f1 and f3 can also be obtained as crosstalk, and,when the pilot signals are added to the reference signal 106 in themixer 115, the beat signals fA and fB can be obtained from aboveformulas (1) and (2) such as f2-f1=fA and f2-f3=-fB.

Next, the output signal of the mixer 115 is fed through the amplifier116 and the divider circuits 117 and is extracted in the band passfilters 118a and 118b. Then, the filtered signals are detected in theenvelope detector circuits 119a and 119b. At this time, while themagnetic head 109 scans on-track along the track of the signal f2, whenthe magnetic head 109 is shifted a slight amount toward the f1 side, thebeat signal fA increases, or a slight amount toward the f3 side, thebeat signal fB increases, and hence the output signal of thedifferential amplifier 120 can be output as the tracking control signal121.

In the conventional magnetic recording and reproducing apparatus asdescribed above, high density recording or reproducing is carried out,and a tracking system with extremely narrow tracks is provided. Hence,in this case, a device capable of detecting a track shift with highaccuracy is required, and in general, as described above, by recordingthe low frequency pilot signals, the track shift can be detected.However, in the case of digital magnetic recording, there is a powerspectrum extending over a wide frequency range from near direct currentto a maximum recording frequency in usual recording and reproducing, andthus a gap in the so-called frequency allocation can not be formedoutside the range of a carrier and its periphery as in conventionalanalog FM recording. In particular, in a digital recording, it isdifficult to insert a low frequency pilot signal for tracking into a gapin the frequency allocation like present analog 8 mm VTR.

When the power level of the pilot signal recorded in the frequency rangeof the pilot signal for tracking is large enough compared with the powerlevel of the recording signal obtained by modulating the digital dataeven in the digital recording, the pilot signal for tracking can beextracted by a band pass filter or the like and reproduced in the samemanner as a conventional example.

However, in the case where the power level of the pilot signal isenlarged too much with reference to the recording or reproducing signalof visual or audio data as described above, when the signal isdemodulated during reproducing, the wave form deformation is enlargedand the error rate of the digital data increases. Particularly, when thedigital data after the modulation and the pilot signal for tracking areadded in an analog way before being input to the recording amplifier,since there is no relationship between the digital data and the pilotsignal, the two signals mutually act as only disturbance signals.

That is, in a digital data recording and reproducing apparatus such as adigital audio recorder or a digital video recorder, the frequencyspectrum of a recording or reproducing signal includes many lowfrequency components due to a feature of digital recording, and, when alow frequency pilot signal for tracking is added to the recording orreproducing signal to record the added signal, since there is norelationship between the recording or reproducing signal and the pilotsignal, a wave form deformation is caused when demodulating themodulated digital signal, and the data error rate increases.

In order to reduce the wave form deformation caused in the demodulating,the power level of the pilot signal is lowered, and a necessary S/Nratio for a servo (tracking) detection signal can not be obtained.Accordingly, the servo can not be given, and the recording density inthe tracking direction in the magnetic tape can not be gained.

In FIG. 6, there is shown a conventional rotary magnetic head device, asdisclosed in Japanese patent laid-open No. Sho 58-47383. FIG. 7 shows atrack pattern recorded on a recording medium such as a magnetic tape bythe rotary magnetic head device shown in FIG. 6, and in this instance,the recording is carried out without any guard band, adjacent two trackshaving different azimuth angles. As shown in FIG. 6, two double azimuthheads 202 each composed of a pair of heads H_(L1) and H_(H1) or H_(L2)and H_(H2) having different azimuth angles are arranged on the peripheryof a rotary drum 201. The pairs of heads H_(L1), H_(H1), H_(L2) andH_(H2) are aligned in opposite positions through 180° with reference tothe central axis of the rotary drum 201, and the pair of heads H_(L1)and H_(H1), or H_(H1) and H_(H2) are arranged at a distance away fromeach other corresponding to 6H (H means a horizontal scanning period)time. A recording medium 203 such as a magnetic tape is wound aroundapproximately half the rotary drum 201.

The operation of the conventional rotary magnetic head device shown inFIGS. 6 and 7 will now be described in detail.

First, in a recording mode, a composite color signal composed of aluminance signal and a color signal multiplied by each other is dividedinto two system signals such as a low range signal SL including a signalrepresenting a brightness component and a high range signal SH includinga color signal component (carrier color signal) and a high rangeluminance signal component, and the low and high range signals SL and SHare frequency-modulated. Then, the modulated low and high range signalsare input to the double azimuth head 202 composed of two heads H_(L1)and H_(H1) or H_(L2) and H_(H2) arranged on the rotary drum 201 and arerecorded in two channels on the recording medium 203. In this instance,the divided two range signals SL and SH are passed through two differentsystems, and hence their delay times can be different on reproducing.Hence, a timing-axis adjustment may be required, and as referencesignals for the timing-axis adjustment, a burst signal and a horizontalsynchronizing pulse (PH) are used for the low range signal SL and thehigh range signal SH, respectively. The PH signal is a low frequencysignal with negligible azimuth effect. As a result, as shown in FIG. 7,by determining the head distance between the two heads H_(L1) and H_(H1)or H_(L2) and H_(H2) to 6H, the H-alignment is achieved in the trackingpattern recorded on the recording medium 203. Hence, even when thecrosstalk is increased in the P_(H) portions by mistracking, suchsections correspond to the horizontal blanking periods, and no imagequality deterioration by the crosstalk will be caused.

However, in the conventional rotary head device as described above, whenthe head device is applied to the digital recording, there is no signalcorresponding to the horizontal synchronizing signal, and thus anappropriate tracking error signal can not be obtained. Further adetermination of the head interval in the double azimuth head is newlyrequired.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a dataconversion method in view of the above-described problems of the priorart, which is capable of controlling a DSV value every code word, andreducing relatively low frequency components in a spectrum of a codeword to achieve a DC free data conversion

It is another object of the present invention to provide a pilot signalformation method for forming a tracking error signal in a magneticrecording and reproducing system, in order to prevent problems of theprior art, which is capable of largely reducing wave form deformation indemodulating a signal by adding pilot signals to a data signal,obtaining a large S/N ratio of a servo detection signal and narrowing atracking pitch to achieve high density recording and reproducing.

It is a further object of the present invention to provide a rotarymagnetic head device for use in a magnetic recording and reproducingapparatus using a double azimuth head, free from the aforementioneddefects and disadvantages of the prior art, which is capable ofobtaining an appropriate tracking error signal for use in narrowing thetracking pitch to realize high density recording and reproducing, andobtaining a suitable determination condition of the distance between thetwo heads constituting the double azimuth head.

In accordance with one aspect of the present invention, there isprovided a data conversion method from m bits of data words into n bitsof code words, n being larger than m, comprising restricting the numberof bits with a value "0" arranged between one bit value "1" and anotherbit value "1" to at most 4 in a code string of each 16 bit code word;allowing a pair of groups of the n bits of code words corresponding toCDSs (code word digital sum) of two codes +1 and -1 to correspond to them bits of data words; and selectively using one of the two codes +1 and-1 according to a DSV (digital sum variation) control signal to convertthe m bits of data word into the n bits of code word.

In accordance with another aspect of the present invention, there isprovide a pilot signal formation method for obtaining a tracking errorsignal in a magnetic recording and reproducing apparatus in whichdigital signals are recorded or reproduced onto or from a magneticmedium by using a rotary magnetic head device mounted on a rotary drum,comprising allowing a pair of groups of n bits of code wordscorresponding to CDSs (code word digital sum) of two codes +1 and -1 tocorrespond to m bits of digital signals in a data conversion from the mbits of two-value digital signals into the n bits of code words, n beinglarger than m, in a recording; and controlling a DSV (digital sumvariation) of a string of digital data by using a selected one of thetwo codes +1 and -1 according to a DSV control signal, an initial phaseof the DSV control signal being preset by a signal synchronized with adrum PG signal for controlling the phase of the drum to form a pilotsignal synchronized with the digital data.

In accordance with a further aspect of the present invention, there isprovided a pilot signal formation method for obtaining a tracking errorsignal in a magnetic recording and reproducing apparatus in whichdigital signals are recorded or reproduced onto or from a magneticmedium by using a rotary magnetic head device mounted on a rotary drum,comprising allowing a pair of groups of n bits of code wordscorresponding to CDSs (code word digital sum) of two codes +1 and -1 tocorrespond to m bits of digital signals in a data conversion from the mbits of two-value digital signals into the n bits of code words, n beinglarger than m, in a recording; selecting of two kinds of DSV (digitalsum variation) control signals, formed by counting a code conversioncycle, by a drum PG signal for controlling the phase of the drum; andmaking the DSV at the end of the code word 0 every predetermined cycleby using a selected one of the two codes +1 and -1 according to theselected DSV control signals to form two kinds of pilot signals so thatthe frequency of the pilot signal is alternately changed every recordingtrack.

In accordance with still another aspect of the present invention, thereis provided a rotary magnetic head device for use in a magneticrecording and reproducing apparatus, comprising a double azimuth headincluding a pair of head members having different azimuth angles forrecording and reproducing a two-channel signal obtained by multiplying adata signal with a pilot signal, wherein an interval of the two headmembers is an integral number of times as much as approximately awavelength of the pilot signal.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will more fully appear from the following description of thepreferred embodiments with reference to the accompanying drawings, inwhich:

FIG. 1 is a schematic block diagram of a circuit structure for aconventional data conversion system;

FIG. 2 shows a data conversion table used in the data conversion systemshown in FIG. 1;

FIG. 3 is a schematic chart for explaining the operation of the dataconversion system shown in FIG. 1;

FIG. 4 is a schematic block diagram of a pilot signal formation circuitand tracking error detection circuit for forming a tracking error in aconventional magnetic recording and reproducing apparatus;

FIG. 5 shows a relationship between a recording medium and a magnetichead movable thereon for use in the conventional system shown in FIG. 4;

FIG. 6 shows a conventional rotary magnetic head device arranged on arotary drum;

FIG. 7 shows a relationship between a recording track pattern recordedon a recording medium and the rotary magnetic head device shown in FIG.6;

FIG. 8 is a circuit diagram of a data conversion system according to thepresent invention;

FIG. 9 shows code word numbers obtained under certain conditions in thedata conversion system shown in FIG. 8;

FIGS. 10(a)(1) and 10(a)(2), hereinafter collectively referred to asFIG. 10(a); 10(b)(1) and 10(b)(2), hereinafter collectively referred toas FIG. 10(b); 10(c)(1) and 10(c)(2), hereinafter collectively referredto as FIG. 10(c); 10(d)(1) and 10(d)(2), hereinafter collectivelyreferred to as FIG. 10(d), show a code conversion table for use in thedata conversion system shown in FIG. 8;

FIG. 11 is a schematic chart for explaining an operation of the dataconversion system shown in FIG. 8;

FIG. 12 is a graphical representation showing a power frequency spectrumof a signal obtained in the data conversion system according to thepresent invention;

FIG. 13 is a graphical representation showing another power frequencyspectrum of a signal obtained in the data conversion system according tothe present invention;

FIG. 14 is a block diagram of one embodiment of a pilot signal formationcircuit for forming a tracking error in a magnetic recording andreproducing apparatus according to the present invention;

FIG. 15 shows code words of original data for use in the circuit shownin FIG. 14;

FIGS. 16 and 17 are timing charts of a DSV value of a code wordaccording to the present invention;

FIG. 18 is a schematic chart for explaining an operation of the circuitshown in FIG. 14;

FIG. 19 is a graphical representation showing a power frequency spectrumof a code string obtained in the circuit shown in FIG. 14;

FIG. 20 shows recording tracks and magnetic heads for recording thetracks in the circuit shown in FIG. 14;

FIG. 21 is a timing chart showing an error signal formation from pilotsignals according to the present invention;

FIG. 22 shows a relationship among phases of pilot signals of adjacenttracks according to the present invention;

FIG. 23 is a time chart showing wave forms appearing in the circuitshown in FIG. 14;

FIG. 24 is a block diagram of another embodiment of a pilot signalformation circuit and a tracking error detection circuit for forming atracking error in a magnetic recording and reproducing apparatusaccording to the present invention;

FIG. 25 is a schematic chart for explaining an operation of the circuitshown in FIG. 24;

FIG. 26 shows a relationship between a recording medium and a magnetichead movable thereon for use in the circuit shown in FIG. 24;

FIG. 27 shows one embodiment of a rotary magnetic head device accordingto the present invention;

FIG. 28 shows a relationship between a recording track pattern recordedon a recording medium and the rotary magnetic head device shown in FIG.27;

FIG. 29 shows wave forms of pilot signals picked up by the rotarymagnetic head device according to the present invention; and

FIG. 30 is a synchronous detection circuit of the pilot signals shown inFIG. 29.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described with reference to theaccompanying drawings, wherein like reference characters designate likeor corresponding parts throughout the several views and thus therepeated description thereof can be omitted for brevity.

Now, codes satisfying the conditions that a data word length m=12 ; acode word length n=15 ; and Tmax/Tmin=5, will be formed. In this case,it is defined that d (the minimum number of "0" between any "1" and thenext "1")=0, and k (the maximum number of "0" between any "1" and thenext "1")=4. The NRZI (non-return-to-zero inverse)(F) rule is applied tothe codes. Hence, in order to satisfy k=4, the maximum number ofcontinuous "0" in each code word is at most 2 in the MSB (mostsignificant bit) side and the LSB (least significant bit) side and isalso at most 4 within the code word itself. In this case, in the codewords in which the MSB starts from "0", the code word numbers satisfyingthe "0" run-length condition are shown in FIG. 9.

In this embodiment, although the data word length m and the code wordlength n (n>m) are selected to 12 and 15, respectively, the presentinvention is not restricted to these values, and any numbers can, ofcourse, be used within the scope of the present invention.

Now, in order to form DC (direct current) free codes, by consideringcode words having different polarities of the CDS (code word digitalsum) as one pair, 2¹² (4096) codes are sufficient. The code word numbersshown in FIG. 9 are only of the code words whose MSB is "0". Hence, byreplacing the MSB with "1" in place of "0", the code words having theinverse polarity of CDS and satisfying the "0"run-length condition canbe obtained. Consequently, only by the use of the above-described codewords with CDS=±1, can the data words=2¹² (4096)<code word number=4616be obtained. By using only the code words with the MSB="0"and the CDS=±1and controlling the MSB to either "0" or "1", the divergence of the DSV(digital sum variation) can be suppressed. Also, the control of the MSBcan be settled by checking up the CDS data ("1" by +1 and "0" by -1) ofthe code words converted right before and the level data ("1" at highlevel and "0" at low level) at the end of the code word after the NRZImodulation on the basis of a control signal command. Thus the obtainedcode conversion table is shown in FIGS. 10a to 10d.

In FIGS. 10a to 10d, two-value digital signals are shown by hexadecimalcodes. As to the 12 bits of input data words, when the MSB of the codeword is "0", the CDS data is represented by 1 bit, and the level data(hereinafter referred to as "Q" and the start end of the code wordstarts from 0 level) at the end of the code word after carrying out theNRZI modulation of the converted serial data is represented by 1 bit,and the remaining 14 bits correspond to the LSB to the 14th bit of thecode word.

In FIG. 8, there is shown one embodiment of a data conversion systemaccording to the present invention. An encoder 3 includes the codeconversion table shown in FIGS. 10a to 10d. The encoder 3 receives 12bits of digital data or data words and converts the data words into 16bits of digital data or code words shown in the code conversion tableshown in FIGS. 10a to 10d. A MSB controller 4 includes four EXORcircuits A, B, C and D and a one symbol (code word) delay circuit 4a.The MSB controller 4 receives CDS and Q output from the encoder 3 and aDSV control signal command and outputs a signal Y representing a MSBlevel. A parallel-serial (P/S) converter 5 receives 14 bits of codewords output from the encoder 3 and the signal Y output from the MSBcontroller 4 and converts 15 bits of parallel data into a serial datastring to output a serial code word to an NRZI modulator 6. The NRZImodulator 6 processes the serial data string of the code word so as torepeat an inversion every "1" level to output a modulated signal. InFIG. 11, there are shown signals at the points (e), (f), (g), (h), (i),(i'), (Y), ((Y)+(J)) and (k) which appear in FIG. 8 along with (l) DSVvalues at the end of a code word.

The operation of the data conversion according to the present inventionwill now be described in detail in connection with FIGS. 8 to 11.

First, in the initial set state, the output (i') of the 1 symbol delay4a of the MSB controller 4 and the output of the NRZI modulator 6 arereset to a "0" level. In this state, when a data word (e) of FDF isinput to the encoder 3, the encoder 3 outputs 14 bits of code wordcomposed of the LSB to the 14th bit, 1 bit of CDS signal and 1 bit of Qsignal corresponding to the code word in the form of a total of 16 bitsof signal of 3FC9 obtained by the code conversion table shown in FIGS.10a to 10d.

The detail of the 16 bits of signal of 3FC9 is as follows. That is, theMSB bit of the 4 bits 0011 of 3 is the Q signal for the code word, and"0" and "1" represent a low level and a high level, respectively, of theend of the code word after the NRZI modulation when the MSB of the codeword is "0" (the start end of the code word starts from a low level inthe NRZI modulation). The second bit from the MSB of the 4 bits 0011 of3 is the CDS signal of the code word, and "0" and "1" represent -1 and+1, respectively, when the MSB of the code word is "0". The lower twobits of the 4 bits 0011 of 3 correspond to the 14th and 13th bits of thecode word. Then, 4 bits 1111 of F, 4 bits 1100 of C and 4 bits 1001 of 9successively correspond to 12th to 9th bits, 8th to 5th bits and 4th tothe LSB, respectively, of the code word.

The 14 bits of code word (j) are sent to the P/S converter 5, and the Qsignal (h) and the CDS signal (g) together with the DSV control signalcommand (f) are fed to the MSB controller 4. In the MSB controller 4,the MSB of the code word is determined as hereinafter described indetail and is output as the Y signal to the P/S converter 5.

The DSV control signal command (f) is set to "1" (high level) or "0"(low level) when the divergence of the DSV is carried out in the (+)direction or the (-) direction, respectively. In this embodiment, asshown in FIG. 11, relating to the data word of FDF, the DSV controlsignal command (f) is output so that the DSV may diverge in the (-)direction, and hence it is required to control the code word so that theCDS may be (-) in the code string. Thus, in the MSB controller 4, bychecking up the output (i') of the 1 symbol delay 4a which represents"0" or "1" when the level of the end of the code word after the NRZImodulation of a just preceding code word is low or high, respectively,it is checked by the EXOR circuit A whether or not the divergencedirections of the CDS and the DSV are coincident with each other whenthe MSB of the code word to be output at present is "0". When thedivergence directions of the CDS and the DSV are coincident or notcoincident, the output of the EXOR circuit A is "0" or "1",respectively, thereby operating so that the CDS of the code word may becoincident with the divergence direction command of the DSV when theNRZI modulation of the MSB of the code word is carried out from the lowlevel.

Then, the output of the EXOR circuit A and the output (i') of the 1symbol delay 4a are fed to the EXOR circuit B. When the output (i') is"0" (that is, the end of the just preceding code word is ended as thelow level after the NRZI modulation), the output of the EXOR circuit Ais output as the MSB signal (Y) of the code word from the EXOR circuit Bas it is. On the other hand, when the output (i') is "1". (that is, theend of the just preceding code word is ended as the high level), sincethe polarity of the CDS of the code word is inverted during the NRZImodulation, thus the output of the EXOR circuit A is inverted in theEXOR circuit B, and the inverted output of the EXOR circuit A is outputas the MSB signal (Y) of the code word from the EXOR circuit

By applying the above-described operation to one embodiment, as apparentfrom FIG. 11, when the data word of FDF is input to the encoder 3, theDSV control signal command (f), the CDS (g), the output of the EXORcircuit A, and the output (i') of the 1 symbol delay 4a are all "0", andthe output of the EXOR circuit B is also "0" to output the MSB of thecode word.

As described above, the 12 bits of data word are converted into 15 bitsof code word according to a divergence direction command of a DSV.Further, as described above, it is necessary to check the level of theend of the code word after the NRZI modulation, and this checking iscarried out as follows.

When the MSB of the code word is "0", the Q signal (h) and the MSBsignal (Y) of the code word are input to the EXOR circuit C of the MSBcontroller 4. When the MSB of the code word is "0", the Q signal isoutput from the EXOR circuit C as it is. On the other hand, when the MSBof the code word is "1", since the code word is inverted during the NRZImodulation process, the Q signal is inverted in the EXOR circuit C, andthe inverted Q signal is output from the EXOR circuit C. Then, theoutput of the EXOR circuit C and the output (i') of the 1 symbol delay4a, which represents the level of the end of the just preceding codeword after the NRZI modulation, are fed to the EXOR circuit D.

In the case where the output (i') is "0" (that is, the level of the endof the just preceding code word after the NRZI modulation is low), whenthe code word now being converted is continuous to the Just precedingcode word, the level of the end of the code word after the NRZImodulation becomes The output level of the EXOR circuit C. Hence, theoutput of the EXOR circuit C is output, as it is, from the EXOR circuitD to the 1 symbol delay 4a for use as an end level signal for the Justfollowing code conversion after the NRZI modulation of the Justpreceding code word. On the other hand, in the case where the output(i') is "1" (that is, the level of the end of the just preceding codeword after the NRZI modulation is high), when the code word now beingconverted is continuous to the just preceding code word, it is necessaryto convert the output of the EXOR circuit C, to that obtained when thelevel of the end of the code word after NRZI modulation starts from thehigh level. Hence, the output of the EXOR circuit C is inverted in theEXOR circuit D, and the inverted output is output from the EXOR circuitD to the 1 symbol delay 4a for use as the end level signal for the justfollowing code conversion after the NRZI modulation of the Justpreceding code word.

By showing the aforementioned operation with one embodiment, when thedata word of FDF is input to the encoder 3, the output (i'), the Qsignal (h) of the encoder 3, the output (Y) of the EXOR circuit B, andthe output of the EXOR circuit C are all "0". Further, the output (i')and the output of the EXOR circuit D become "0", which is coincidentwith the fact that the level of the end of the converted code word afterthe NRZI modulation is low.

The above-described operation is repeated every code word conversion,and the 1 symbol delay is carried out. Accordingly, the level check ofthe end of the code string in the continuous code word string can becorrectly carried out.

Thus the obtained 15 bits of code word is input to the P/S converter 5and is converted into a string of serial signal or serial code wordstherein, as shown in the form of a signal ((Y)+(j)) in FIG. 11. Theobtained serial signal is fed to the NRZI modulator 6 which outputs anNRZI-modulated signal (k), as shown in FIG. 11.

Then, the data words of "000", "011", "015", "FFC", "003", "005", . . .are converted into code words shown as the signal ((Y)+(j)) in FIG. 11while the DSV control is carried out by the DSV control signal command(f) in the same manner as described above, and then the NRZI modulationof the code words is carried out in the NRZI modulator 6 to output thesignal (k). The DSV value of the end of each code word in the outputsignal (k) is within a variation width of ±1 at a 4 code word cycle, asshown in FIG. 11(l), and thus the code words can be obtained as signalssynchronizing with the DSV control signal command.

In this embodiment, although the code word (j) composed of the LSB tothe 14th bit of the 16 bits of the converted code in the code conversiontable shown in FIGS. 10a to 10d is output by the encoder 3 and the MSBis decided by the MSB controller 4 to Carry out the data conversion fromthe 12 bits of data word into the 15 bits of code word, two groups of 15bits of code words composed of a pair of ± code words groups can beprepared, and one of the groups can be selected by the DSV controlsignal command (f) and the level signal of the end of the just precedingcode word after the NRZI modulation so as to directly output 15 bits ofcode word.

Further, in this embodiment, although an example where the code word isfurther NRZI-modulated is output has been described, after the P/Sconversion of the code word, the obtained string of serial code word canbe output as it is. In this instance, by using only code words whoserun-length codes satisfies at least 2 (3) continuous bits of the samelevel in the MSB side, at least 3 (2) continuous bits of the same levelin the LSB side and at least 5 continuous bits of the same level withinthe code word itself and the CDS value is either +1 or -1 obtained at"1" or "0" level, respectively, each pair of code words having differentpolarities of the CDS are allowed to correspond to one data word, andone of each pair of code words is selected according to the DSV controlsignal command (f) with the same effects as the above-describedembodiment.

As described above, according to the present invention, the number ofthe same level of continuous codes within the code word after the NRZImodulation is at least 5, and the coding is carried out by using onlythe code words with the CDS of ±1 while the CDS value is controlled soas to suppress the divergence of the DSV according to the DSV controlsignal command. Hence, a data conversion system having a largesuppression effect against a relatively low frequency range can beachieved compared with a conventional data conversion system.

According to the present invention, by allowing a pair of code wordshaving CDSs of ±1 to correspond to one data word, a DSV control can befreely carried out every code word unit, and hence suppression of arelatively low frequency range can be realized.

FIGS. 12 and 13 show power spectra obtained according to the presentinvention. That is, a circuit is constructed by one embodiment of a dataconversion system of the present invention, and random signals of Mseries represented by a formula of (X²³ +X⁵ +1) are partitioned every 12bits and are input to the circuit to obtain the power spectra. FIG. 12shows a spectrum extending from 0 Hz to a frequency of a signal forcarrying NRZI modulation data. In this case, frequency components lessthan 0.05×fcH (carrier frequency) are suddenly damped to accomplish a DCfree modulation. FIG. 13 shows a spectrum extending from 0 Hz to afrequency of 0.1×fcH. In this case, the DC free modulation is achieved,and it is apparent that a strong spectrum only in the frequencies of theDSV control signal command cycle can be obtained.

Further, the signals of the DSV control signal command cycle can beextracted by a band pass filter, and hence the signals can be used asthe second signal synchronizing with the digital signal. For instance,when the present invention is applied as a data converter to a magneticrecording and reproducing apparatus in which digital signals arerecorded or reproduced onto or from a magnetic tape by using a rotarydrum, such signals can be used as pilot signals for a head to correctlyscan along recording tracks in the reproducing mode.

Next, one embodiment of a pilot signal formation circuit for realizing apilot signal formation system according to the present invention willnow be described in detail in connection with FIGS. 14 to 23. In thiscase, data conversion is carried out in the same manner as describedabove with reference to FIGS. 8 to 13.

As shown in FIG. 14, an encoder 124 having a code conversion table shownin FIG. 15 carries out data conversion from 12 bits of parallel inputdigital signal or data word into a 15 bit parallel digital signal orcode word, charge storage (CDS) within the code word allowing a pair ofcode words having different polarities of -1 and +1 to correspond to oneinput digital signal. A flip flop 125 outputs a DSV control signal forsetting the CDS value of the code word output from the encoder 124. Acounter 126 for counting up a code conversion cycle (SYCK) is providedwith a load terminal for input of a preset count value, a set inputterminal of 3 bits and a CY output terminal for outputting a 1 level tothe flip flop 125 when the count value is 7.

A parallel-serial (P/S) converter 127 converts the 15 bits of parallelcode word fed from the encoder 124 into a string of serial code words tobe transferred at a serial data transfer frequency (fcH). A recordingamplifier 128 capable of supplying a certain current even on a low loadreceives the serial code word from the P/S converter 127 and outputs anamplified signal to a double azimuth magnetic head 129 arranged on arotary drum 134. The double azimuth head 129 includes two heads A and Bhaving different azimuth angles. A recording medium 130 such as amagnetic tape is wound around approximately half the rotary drum 134.

An initial phase adjuster circuit 131 synchronized with the rotation ofthe rotary drum 134 receives a drum PG (DPG) signal, generated by asensor (not shown) mounted to the rotary drum 134, for generating onepulse per one rotation of the rotary drum 134 and the SYCK and sets aninitial phase of a pilot signal at a recording start point every onerotation of the rotary drum 134. A selector 132 selectively outputssignals to the set input terminal and the load terminal of the counter126. A cycle set 133 for setting the cycle of the counter 126 outputs 3bits of signal to one terminal of the selector 132. The above-describedcomponents, except the double azimuth head 129 and the rotary drum 134,constitute an A-channel (Ach) circuit section 135A. A B-channel (Bch)circuit section 135B having the same structure as the A-channel circuitsection 135A (and thus its detailed description is omitted for brevity)is also provided.

In this embodiment, although the data word length m and the code wordlength n (n>m) are selected to 12 and 15, respectively, the presentinvention is not restricted to these values, and any numbers can, ofcourse, be used within the scope of the present invention.

The operation of the system shown in FIG. 14 will now be described indetail in connection with FIGS. 14 to 23.

In FIG. 14, 12 bits of digital signal are input to the encoder 124 andconverted therein into 15 bits of code word selected from one of a pairof code word groups corresponding to a pair of CDSs of ±1 in a codeconversion table shown in FIG. 15 according to the DSV control signaloutput from the flip flop 125. The obtained code word is output from theencoder 124 to the P/S converter 127. FIG. 16 shows, for example, 15bits of code word obtained from an input digital signal of 001(hereinafter indicated in the same manner as a parallel signal such as012, . . . , EF) according to the code conversion table shown in FIG.15, output from the encoder 124, and also shows the charge storage of astring of the code word output from the encoder 124 when the DSV controlsignal is 0 level. It is clear from FIG. 16 that the charge storage orthe level of the end of the code word is -1.

FIG. 17 shows another 15 bits of code word obtained from an inputdigital signal of 001 output from the encoder 124 when the DSV controlsignal is 1 level, and also shows the charge storage of a string of thecode word. It is readily understood that the level of the end of thecode word is +1. The charge storage or CDS within the code word iseither -1 or +1 for all code words, as shown in FIG. 15, and the CDS atthe end of the code word is properly controlled to -1 or +1 by theoutput level or the DSV control signal output from the flip flop 125.Hence, for example, as shown in a timing chart in FIG. 18, the counterpreset value of the counter 126 which counts up to every SYCK, is set to3, and the CY output of the counter 126 to which the preset value isrepeatedly loaded by the CY output at the count value of 7, is fed tothe flip flop 125. The flip flop 125 divides the CY output frequency to1/2, and by controlling the CDS by the 1/2 frequency-divided signal, thecode string having a cycle of ten times as large as the SYCK and theDSV=5 at the end can be obtained in the encoder 124.

The power spectrum of the digital signal having two-values such as 1 and0 can be decided by the appearance of a state transition probabilitydiagram. For example, in the case of the random digital signal in Msystem, the power spectrum is approximately flat in the frequency rangefrom DC to a carrier clock signal frequency. On the other hand, like thepresent invention, in the code string where the DSV is regularly andcorrectly varied at a fixed cycle, in cooperation with the limited DSV,a signal having no DC component and having a spectrum resistant to DSVfrequency can be obtained.

FIG. 19 shows a power spectrum obtained as follows. That is, under theconditions where the CDS control cycle of the code word is ten times asmuch as the code conversion cycle, 15 bits of parallel digital signaloutput from the encoder 124 are fed to the P/S converter 127 and areconverted therein into serial data, and the obtained serial data aretransferred at 1/15 of the code conversion cycle to the magnetic head129 through the recording amplifier 128. The power spectrum flowed inthe magnetic head 129 is measured, as shown in FIG. 19, and it isconfirmed that the spectrum resistant to the DSV cycle (1/150 of theseries data carrier frequency fcH) can be obtained. Accordingly, byrecording such a signal onto the magnetic tape 130, a low frequencypilot signal can be recorded in synchronization with a digital signal inthe same manner as a conventional method.

Next, a method of recording a pilot signal formed by the present systemwill now be described in detail with reference to FIGS. 20 and 21.

In FIG. 20, on A channel tracks A0, A1 and A2, a first signal outputfrom the recording amplifier 128 to the double azimuth magnetic head 129composed of two heads A and B is recorded by the head A, and on Bchannel tracks B0, B1 and B2, a second signal having a different DSVcycle from that of the first signal, coded in the same manner asdescribed above, is recorded by the head B. In this case, the distance Lbetween the two heads A and B is 400 to 1000 μm, and the head A precedesa distance an integral number of times as much as the pilot wavelengthfrom the head B.

In this embodiment, what is noteworthy is a 180° shift between thephases of the pilot signals of two tracks A1 and A2 on both sides of thetrack B1, so head B detects the error signal in order to carry out atracking control in the reproducing mode. In recording such pilotsignals, as shown in FIG. 21, when the head B is on-track in the centerof the track B1, the pilot signals picked up by the head B from the twotracks A1 and A2 adjacent to the track B1 as the head B scans are zero,and, when the head B is off-track in the direction of the track A1, thephase is the same as that of the pilot signals picked up by thepreceding head A, or when the head B is off-track in the direction ofthe track A2, the phase is reverse to that of the pilot signals pickedup by the head A. Therefore, by carrying out a synchronous detection ofthe pilot signals picked up by the head B by using the pilot signalspicked up by the head A, when the head B is on-track, zero is obtained,and when the head B is off-track in the direction of either track A1 orA2, either (+) or (-) tracking error signals can be formed. Hence, byusing the thus obtained tracking error signal, the tracking control inthe reproducing mode is possible in the same manner as a conventionalmethod.

In the present system, as described above, by recording the pilotsignals on every other track so that the phases of the pilot signals maybe inverted through 180° every recording of the pilot signal on thetrack, as shown in FIG. 20, when the head is on-track, the crosstalk ofthe pilot signals disappears, and hence the disturbance on reproducingthe digital signal is removed.

Then, the obtained pilot signals are recorded under the above conditionsas follows. As shown in FIG. 20, for example, assuming that a trackslant angle is θ and a track pitch is TP, the head B picks up signalshaving a track step difference LT=(2TP/tanθ) between the recording startpoints of the two tracks A1 and A2 adjacent to the track B1 the head Bnow scans and picks up the pilot signals from the two tracks A1 and A2.Accordingly, it is necessary to control the DSV phase so that the phaseof the pilot signal of the track A2 may be reversed to the phase of thepilot signal of the track A1 at the point (2TP/tanθ) from the recordingstart point.

On the other hand, assuming that the relative speed of a head withrespect to a tape is Vh, a wavelength λ(PILOT) of a pilot signal isexhibited as λ(PILOT)=(Vh/DSV) cycle, and the resolution of phasecontrol becomes (360°/DSV) cycle coded block number X. In this case, theDSV cycle is, of course, the same as the aforementioned CDS controlcycle.

Therefore, in order to settle the phase difference of 180° between thepilot signals of the tracks A1 and A2 with reference to the head B, thephase difference Δφ1 between the pilot signals due to the track step,difference LT is obtained under the condition of LT>λ(PILOT)·P (P:integer) as follows.

    Δφ1=(LT-λ·P/λ)·360°

Then, the phase control amount Δφ2 for achieving the phase difference of180° is calculated as follows.

    Δφ2=Δφ1-180°

On the other hand, in the present system, the resolving power of thephase control of the pilot signal is (360°/DSV) cycle coded block numberX, as described above, and it is enough to shift the phase of the DSVcontrol signal for a value of Y of which |Δφ2-(360/X)·Y| becomes theminimum. In this instance, Y is an integer satisfying Y≦(X/2).

Next, the operation of the phase control will be described morespecifically in connection with FIG. 22 in which specific values aresubstituted for parameters for better understanding. Now, with thecomparative speed Vh=9.4 m/sec, the coding frequency=2.28 MHz and theDSV cycle=10 coded block, the DSV frequency, i.e., the pilot frequencybecomes 2,74 MHz/10=228 KHz, and the wavelength of the pilot signalλ(PILOT)=9.4/(228×10³)=41.28 μm. Further, with the track pitch TP=6.1 μmand the track slant angle θ=4.69°, the track step difference LT betweenthe tracks A1 and A2 becomes 2.61 μm/tan4.69°=148.71 μm.

Hence, according to the above formulas, the phase difference Δφ1 iscalculated to obtain 218.46°, and the phase control amount Δφ2 is218.46°-180°=88.46°. On the other hand, the phase control resolution ofthe DSV control is (360°/10) block=36°, and Y of which |Δφ2-(360/X)·Y|the minimum is 1.

Accordingly, when the DSV initial phase signal of the pilot signalstarts from 0 at the start of the recording of the track A1, by startingfrom 1 in the track A2, the pilot signals of the tracks A1 and A2 withthe 180° phase difference therebetween with reference to the head B canbe recorded. Then, for the track A3 to the track An, the recording ofthe pilot signals can be carried out by starting from a number which isobtained by adding +1 to the DSV initial phase signal value of thepreceding track in the same manner as described above.

Hence, as a specific circuit operation, as is apparent from FIG. 23, bycounting up a counter in the initial phase adjuster circuit 131 withY=Y+1 by the DPG pulse signal generated every one rotation of the rotarydrum in synchronization with the rotation of the rotary drum, theselector 132 is switched to preset the initial phase value in thecounter 126 just before the recording start. For instance, when thetrack A1 is recorded, 3 of 0+3 (3 is an offset value for outputting CYfrom the counter 126 at the count value of 7) is output from the initialphase adjuster circuit 131 to the counter 126, and, when the track A2 isrecorded, 4 is output from the initial phase adjuster circuit 131 to thecounter 126. Then, the counter within the initial phase adjuster circuit131 is counted up by Y in every X/2 base every one rotation of therotary drum in the same manner as described above. Further, every carrysignal in the counting, it is required to set and reset the flip flop125 for deciding the initial polarity of the DSV by the initial polarityset signal.

After the initial phase value is loaded to the counter 126, the counter126 is counted up by the SYCK of the code conversion rate and outputsthe signal CY at the count value of 7. The signal CY is input to theflip flop 125, and the DSV control signal is inverted from 0 to 1 orfrom 1 to 0 by the trailing edge of the signal CY. Also, after theinitial phase value is loaded into the counter 126, the selector 132 isswitched together with the cycle set 133 for deciding the DSV phase sothat the the signal CY may be input to the counter 126. Hence, byinputting the cycle set value by the signal CY, the counter 126 isconfigured as a ring counter (of 8-cycle set value) and outputs thesignal CY every time the count value of 7 is reached.

Accordingly, the initial phase value is decided by initial phaseadjuster circuit 131, and then the DSV control signal repeatedlyinverted by the trailing edge of the signal CY is provided with a cycleof (8-cycle set value)×2 coded block number with a 50% duty cycle. Thus,by controlling the CDS of the code word output from the encoder 124 byusing the obtained DSV control signal, the DSV phase with respect to thetrack position can be controlled at will, and the pilot signals having a180° phase difference can be recorded every other track so that phasesof the pilot signals may be inverted through 180° every recording of thepilot signal on the track, as shown in FIG. 20.

In FIG. 24, there is shown another embodiment of a pilot signalformation circuit and a tracking error detecting circuit for use inproducing a tracking error according to the present invention. In thisembodiment, an encoder 124, a P/S converter 127, a magnetic head 129, arecording medium 130 and a rotary drum 134 are the same as those shownin FIG. 14 and the explanation of the same is omitted for brevity.Further, a turnover switch 108, a low pass filter 113, an amplifier 116,a divider circuit 117, a pair of band pass filters 118a and 118b, a pairof envelope detector circuits 119a and 119b and a differential amplifier120 are the same as those shown in FIG. 4 and the explanation of thesame is omitted for brevity.

As shown in FIG. 24, a pair of first and second counters 136A and 136Bcount up the SYCK and output respective first and second DSV clocksignals having different frequencies such as one by an even number ofthe SYCK and a duty ratio of 50%. A selector 137 selects one of thefirst and second DSV clock signals output from the first and secondcounters 136A and 136B according to the drum PG signal.

The operation of the system shown in FIG. 24 will now be described indetail in connection with FIGS. 15, 19, 24, 25 and 26.

In the recording mode, the first counter 136A counts up the SYCK andoutputs the first DSV control signal, and the second counter 186B alsooutputs the second DSV control signal having a different frequency fromthat of the first DSV control signal in the same manner as the firstcounter 136A. Then, the selector 137 selects one of the first and secondDSV control signals according to the drum PG signal and outputs theselected DSV control signal to the encoder 124. In the encoder 124, inaccordance with the first or second DSV control signal output from theselector 137, 12 bits of parallel input digital signal are convertedinto 15 bits of parallel code word selected from one of a pair of codeword groups corresponding to the CDS of ±1, as shown in FIG. 15.

By controlling the CDS of the code word, a code word string having acycle of 2i (i=integer) times as much as the code conversion cycle andthe DSV=i at the end of the code word can be obtained. The obtained 15bits of parallel code word are fed to the P/S converter 127 andconverted therein into serial data by a clock fcH having one fifteenththe cycle of the SYCK, and the serial data is sent to the magnetic head129 through the switch 108 and a recording amplifier (not shown). Themagnetic head 129 records the serial data on the magnetic tape 130. FIG.25 shows the input signal, the DSV control signal and the DSV of therecorded code word when the cycle of the DSV control signal is one tenthof the SYCK, and the DSV of the code word necessarily becomes 0 everyten symbols. That is, the pilot signal having a frequency of one tenthof the SYCK can be recorded.

The power spectrum of the digital signal having two-value such as 1 and0 can be decided by the appearance of a state transition probabilitygraph. For example, in case of the random digital signal in M system,the power spectrum is approximately flat in a frequency range from DC toa carrier clock signal frequency. On the other hand, like the presentinvention, in the code string in which the DSV is regularly andcorrectly varied at a fixed cycle, in cooperation with the limited DSV,a signal having no DC component and having a spectrum resistant to DSVfrequency can be obtained. FIG. 10 shows a power spectrum of the outputof the P/S converter 127, that is, the recording signal obtained underthe condition that the CDS control cycle of the code word is ten timesas much as the code conversion cycle, and it is confirmed that thespectrum resistant to the DSV cycle (1/150 of the series data carrierfrequency fcH) can be obtained. Accordingly, by recording such a signalonto the magnetic tape 130, a low frequency pilot signal can be recordedin synchronization with a digital signal in the same manner as aconventional method. FIG. 26 shows the relationship between therecording tracks 123 recorded on the magnetic tape 130 as describedabove and the magnetic head 129. In FIG. 26, f1 is the frequency of thepilot signal settled by the first counter 136A and f2 is the frequencyof the pilot signal settled by the second counter 136B. The twofrequencies f1 and f2 are different from each other.

Next, in the reproducing mode, when the recording signal is reproducedfrom the magnetic tape 130 by the magnetic head 129, the data signalincluding the pilot signals is reproduced. Since the frequency of thepilot signals is very low compared with the data signal, even in anazimuth recording, the azimuth effect hardly appears, and the pilotsignals of both the adjacent tracks are picked up as crosstalk. Hence,the data signal is reproduced by using one of the pair of magnetic heads129 which records no pilot signal, and the two pilot signals areextracted by using the band pass filters 118a and 118b. Then, theextracted pilot signals are detected in the respective envelope detectorcircuits 119a and 119b, and the detected signals are compared in thedifferential amplifier 120. When the tracking is shifted to the f1 sideor f2 side, a negative or positive signal as a tracking control signal121 is output from the differential amplifier 120. In this case, thecentral frequencies of the band pass filters 118a and 118b are f1 andf2, respectively.

As described above, according to the present invention, the pilotsignals required for the tracking control can be formed by the DSV ofthe digital signal, and the phase of the DSV can be controlled at will.Hence, the pilot signals having a high accuracy can be obtained withoutcausing any disturbance of the digital signal, and the whole system iscarried out using digital signal processing, enabling a reduction in thecost.

Further, since the pilot signal is formed and recorded as a part of therecording data signal in the modulation, the waveform deformation issmall in the digital demodulation, and the large S/N ratio of the servodetection signal can be obtained. Further, the tracking pitch can benarrowed to achieve high density recording and reproducing. Further,since the pilot signals are formed in the modulation at the same time, apilot signal generator and a mixer are not required in the recording,thus simplifying the system.

According to the present invention, by controlling the polarity of a CDSaccording to a DSV control signal by using only code words correspondingto the CDS of ±1, pilot signals of the DSV cycle are synchronized withdigital data in a low frequency range where the power spectrum of thedigital data is rapidly damped.

Further, by recording a digitally-modulated signal including pilotsignals having two different frequencies. by using only code wordscorresponding to CDS ±1, the pilot signals of the DSV cycle aresynchronized with digital data in the low frequency range where thepower spectrum of the digital data is rapidly damped, to obtain a dropin the data error rate due to the pilot signals in the reproducedsignal.

In FIG. 27, there is shown one embodiment of a rotary magnetic headdevice for use in a magnetic recording and reproducing apparatusaccording to the present invention. Of course, this rotary magnetic headdevice is suitable for use in the systems shown in FIGS. 14 and 24.

As shown in FIG. 27, the double azimuth head 204 is composed of twoheads A and B having different azimuth angles, which are arranged on theperiphery of a rotary drum 201 at distance LH apart, LH being an integernumber of times as long as a distance corresponding to approximately onecycle of a pilot signal. A recording medium 203 such as a magnetic tapeis wound around approximately half the rotary drum 201.

Before describing the operation of the rotary magnetic head deviceaccording to the present invention, to aid understanding of theeffectiveness of the rotary magnetic head device of the presentinvention, a high density magnetic recording and reproducing systemachieved by using the rotary magnetic head device according to thepresent invention will be described.

In order to realize the high density magnetic recording, not only mustthe wavelength be shortened but also the tracking pitch is madenarrower. For instance, it is presumed that in allocation of a high areadensity recording coming up to i μm² /bit, narrow tracks such as a linedensity of 100 KBPI and a recording track width (pitch) of 4 μm areaccomplished.

In order to achieve such a narrow track recording, a DTF (dynamic trackfollowing) control for making a reproduction head trace or track on acurved track is required in the reproducing, and it is also necessary torecord a pilot signal for forming an error signal for the DTF control onthe recording track. Further, in the recording of the pilot signal, thewavelength (frequency) should be determined so that the visual or audiodata are sufficiently low compared with the recording range and noamplitude drop accompanied with the azimuth effect of the azimuth headis caused.

Further, in the digital recording, since extremely low frequencycomponents in exist the spectrum to be recorded onto the recordingmedium after the digital modulation, when the pilot signals are added tothe digital-modulated data and the added data are recorded onto therecording medium, on demodulating the digital-modulated data to theoriginal signal, the pilot signals cause disturbance and code errorsincrease during reproduction. In order to avoid this problem, a methodfor recording pilot signals synchronized with the digital data bycontrolling the DSV in the digital modulation on the recording isdisclosed in Japanese patent laid-open No. Hei 1-317280. In this case,the pilot signal of the track being scanned causes no disturbance, butthe crosstalk of the pilot signals from the adjacent tracks becomedisturbance signals and cause code errors in the demodulation.

Hence, according to the present invention, as shown in FIG. 28, thepilot signals are recorded every other track in a different format sothat the phases of the pilot signals may be inverted through 180° everyrecording of the pilot signal on the track, and hence the crosstalk ofthe pilot signals from the two tracks adjacent to the track beingscanned is mutually cancelled out to zero when the head is on-track.Therefore, when the digital-modulated data are demodulated, an excellentdemodulation can be performed without sustaining the influence of any ofthe pilot signals. The present invention can be appropriately applied tothe above-described magnetic recording and reproducing apparatus.

The operation of the rotary magnetic head device according to thepresent invention will now be described in detail in connection withFIGS. 27 to 30.

In FIG. 28, tracks A0, A1 and A2 are recorded by head A of the doubleazimuth head 204, and on the tracks A0, A1 and A2, the digital-modulateddata along with the pilot signals having the frequency f(PILOT) arerecorded in multiple by controlling the DSV. Also, tracks B0, B1 and B2are recorded by the head B of the double azimuth head 204, and on thetracks B0, B1 and B2, no pilot signal is recorded, that is, only thedigital-modulated data are recorded. In this instance, as is apparentfrom the waveforms of the pilot signals recorded on the tracks A1 and A2at the points indicated by a line X shown in FIG. 28, the phases of eachpilot signal is shifted 180° from the two pilot signals either side ofit.

By recording such pilot signals, as shown in FIG. 29, relating to thepilot signals picked up by the head B of the double azimuth head 204from the tracks A1 and A2 adjacent to the head B1 being scanned by thehead B, when the head B is on-track in the center of the track B1, thecrosstalk amounts of the tracks A1 and A2 having 180° different phasesare equal but opposite and thus become zero. On the other hand, when thehead B is off-track in the direction of the track A1 or A2, the pilotsignal recorded on the track A1 or A2 will be output.

Since the track shift is detected as described above, when the head ison-track, the crosstalk becomes zero, and the pilot signals cause nodisturbance in demodulating the digital-modulated data. However,in theon-track condition, no information can be directly obtained from thepilot signals detecting the track shifts, and no error signal fordriving the servo can be formed. Accordingly, for obtaining theinformation for detecting the track shift, the pilot signals picked upby the head A can be used.

In FIG. 28, since the phases of the pilot signals of the tracks A1 andA2 are inverted through 180°, at the points indicated by the line X, thehead B picks up the pilot signals whose levels change from (+) to (-) orfrom (-) to (+) in the track A1 or A2, and one pilot signal which thehead B is off track towards more than the other is used. On the otherhand, the head A scans the track A1. In the double azimuth head 204,when the head A is positioned preceding the distance LH corresponding tointegral number times as much as approximately the wavelength of thepilot signal (f(PILOT)/Vh)(Vh: relative speed of the head with respectto the recording medium) from the head B, as shown in FIG. 29, thesignal picked up by the head A has the same phase as that of the pilotsignal picked up by the head B shifting in the A1 direction. As aresult, an error signal for driving the servo can be formed by a simplemethod as follows.

In FIG. 30, there is shown a synchronous detector circuit for the pilotsignals. The pilot signal picked up by the head B is input to an input(a) leading to a differential amplifier 205 for outputting a normalsignal to an H input of an analog switch 206 and an inverted signal toan L input of the same. Then, the pilot signal picked up by the head Ais input to an input (b) connected to a comparator 207, and the pilotsignal is converted into a High or Low digital signal in the comparatorto output the signal to be used as a switching signal to an SW terminalof the analog switch 206. Hence, the analog switch 206 outputs, as shownin FIG. 29, a (+) level synchronous detection output when the head B isshifted in the A1 direction, or a (-) level synchronous detection outputwhen the head B is shifted in the A2 direction. As a result, the trackshift direction and amount in the synchronous detection outputs, areextracted, and thus this signal can be used as a tracking error signalto carry out the tracking servo-control or the DTF control.

Further, when the distance LH between the heads A and B is out of theabove-described condition, a PLL clock is formed by the output signal ofthe comparator 207, and the phase of the clock signal is controlled tobe the same as or reverse to that of the pilot signal picked up by thehead B to invite an increase of a scale of the circuit.

Although the interval LH between the two heads A and B is set to anintegral number of times as much as approximately the wavelength of thepilot signal f(PILOT)/Vh, even when the polarities (+) and (-) of thesynchronous detection with reference to the track shift are reversed,there is no problem in the formulas, and it is sufficient to set thehead interval LH to the distance approximately corresponding to theintegral number of times as much as 2f(PILOT)/Vh.

As described above, according to the present invention, since thedistance between the heads A and B of the double azimuth head 204 isdetermined to a distance approximately corresponding to an integralnumber of times as much as f(PILOT)/Vh, when the pilot error signal issynchronously detected, the signal processing can be carried out only onthe picked up signals, and the rotary magnetic head device can befabricated at low cost with high accuracy.

When a pilot error signal is formed, a pilot signal picked up by onehead is used as the signal for carrying out synchronous detection, and apilot signal picked up by another head is directly used.

Although the present invention has been described in its preferredembodiments with reference to the accompanying drawings, it it readilyunderstood that the present invention is not restricted to the preferredembodiments and that various changes and modifications can be made bythose skilled in the art without departing from the spirit and scope ofthe present invention.

What is claimed is:
 1. In a system where data is digitally stored on amagnetic storage medium in parallel tracks, a method of trackingcomprising:storing said data in said parallel tracks using code wordshaving a periodically varying DSV (digital sum variation), the trackshaving differing periodic DSVs to enable tracking of a selected paralleltrack, said step of storing including the steps of,i) providing dataarranged in data words of m bits, ii) providing an open loop DSV controlsignal representative of a desired change in DSV to be produced by eachsaid code word, iii) developing a code word of n bits from each saidcode word of m bits, each said code word of n bits having a CDS (codeword digital sum) of known value selected in response to said DSVcontrol signal to control the DSV of a string of the plural code wordsto a desired value under control of said DSV control signal, iv) storingeach of said code words produced in said step of developing on a saidparallel track, thereby producing the desired variation in DSV on thatsaid track, and v) repeating said substeps i)-v) for adjacent trackswith their associated different DSV signals; reading the signalsobtained from the desired track to produce a reproduction signal, saidstep of reading further reading low frequency crosstalk from adjacenttracks caused by said periodically varying DSV of the data contained inthese adjacent tracks; comparing the low frequency crosstalk from saidadjacent tracks to produce a tracking error signal; and controlling thetracking of said desired track from said tracking error signal.
 2. Themethod of tracking of claim 1 wherein said step iii) of developingincludes the substeps of,developing a code word of n-1 bits from eachsaid data word of m bits, monitoring the CDS of each n-1 bit code word,producing a DSV modifying code word bit in response to the monitored CDSof each n-1 bit code word and the open loop DSV control signal, andadding the DSV modifying code word bit to each n-1 bit code word toproduce a n bit code word having a CDS which produces a DSV of desiredvalue as identified by said open loop DSV control signal.
 3. The methodof claim 2 wherein said DSV modifying code word bit is the MSB (mostsignificant bit) of each n bit code word.
 4. The method of tracking ofclaim 1 wherein said step of comparing determines the difference in thesignal strength of the low frequency crosstalk from each of the adjacenttracks to determine the tracking error in said desired track.
 5. Themethod of tracking of claim 4 wherein said differing periodic DSVs ofsaid tracks vary in frequency.
 6. The method of tracking of claim 5wherein said step of storing stores the code words in adjacent tracks toform code word strings have DSVs which vary with different frequencies.7. The method of tracking of claim 6 wherein said parallel tracksinclude alternating even and odd tracks, the DSVs of said odd tracksalternating between first and second differing frequencies.
 8. Themethod of tracking of claim 7 wherein said magnetic storage medium ismagnetic tape;said step of storing utilizing a rotary drum to producesaid parallel tracks.
 9. The method of tracking of claim 8 wherein saiddrum utilized in said step of storing has a pair of heads mountedthereon and produces a pair of adjacent tracks each scan;only a firstone of each said pair of adjacent tracks having a periodically varyingDSV.
 10. The method of tracking of claim 9 wherein the first ones ofadjacent pairs of tracks have periodically varying DSVs of differentfrequencies.
 11. The method of tracking of claim 7 further comprisingextracting the low frequency crosstalk from said reproduction signal bylow pass filtering; andband pass filtering the low frequency crosstalkat said first and second differing frequencies to recover the pilotsignals of the adjacent tracks; said step of comparing the magnitude ofpilot signals of the adjacent tracks to produce the tracking errorsignal.
 12. The method of tracking of claim 11 further comprisingselectively developing a first or second DSV signal depending on thetrack to be recorded;said step of storing being responsive to said stepof selectively developing to store a code word having a CDScorresponding to the change in the developed DSV signal associated witheach data word.
 13. The method of tracking of claim 4 wherein saiddiffering periodic DSVs of said tracks vary in phase.
 14. The method oftracking of claim 13 wherein said step of storing stores said code wordssuch that alternate tracks, when viewed in a direction transverse to thetracking direction, have DSVs that are 180° out of phase with respect toeach other;said step of comparing developing a difference signal fromthe low frequency crosstalk of the adjacent tracks, said differencesignal having a magnitude and phase indicative of the tracking error insaid desired track.
 15. The method of tracking of claim 14 furthercomprising extracting the low frequency crosstalk from said reproductionsignal by low pass filtering;said step of comparing determining anyerror in tracking the desired track from said low pass filteredreproduction signal.
 16. The method of tracking of claim 13 wherein saidstep of storing stores said code words such that alternate tracks, whenviewed in a direction transverse to the tracking direction, have DSVsthat are 180° out of phase with respect to each other;said step ofcomparing developing a substantially D.C. difference signal from the lowfrequency crosstalk of the adjacent tracks, said D.C. difference signalhaving a magnitude and phase indicative of the tracking error in saiddesired track.
 17. In a system where data is digitally stored on amagnetic storage medium in parallel tracks, a tracking systemcomprising:means for storing said data in said parallel tracks usingcode words having a periodically varying DSV (digital sum variation),the tracks having differing periodic DSVs to enable tracking of aselected one of parallel tracks, said means for storing including, meansfor receiving an open loop DSV (digital sum variation) control signalrepresentative of a desired change in DSV to be produced by each saidcode word, different open loop DSV control signals being produced foradjacent parallel tracks, an encoder receiving said open loop DSVcontrol signal and an M bit data word for storing and developing an Nbit code words having a known CDS (code word digital sum) required toproduce the desired variation in DSV as represented by said DSV controlsignal to make the DSV of said code word string correspond to thedesired DSV, said encoder repeatedly developing N bit code words toproduce a code word string having the a DSV which varies as specified bysaid open loop DSV control signal, and recording means for storing eachof said code words selected in said step of selecting on a said paralleltrack, thereby producing the desired variation in DSV on that saidtrack; said means for storing storing said code word strings on adjacenttracks with differing DSVs as specified by said DSV control signals;means for reading the signals obtained from the desired track to producea reproduction signal, said means for reading further reading lowfrequency crosstalk from adjacent tracks caused by said periodicallyvarying DSV of the data contained in these adjacent tracks; means forprocessing the low frequency crosstalk from said adjacent tracks toproduce a tracking error signal; and means for adjusting the tracking ofsaid desired track from said tracking error signal.
 18. The trackingsystem of claim 17 wherein said encoder includes,an n-1 bit encoderdeveloping a code word of n-1 bits from each said data word of m bits,said n-1 bit encoder identifying the CDS of each n-1 bit code word, aDSV modifying bit generator producing a DSV modifying code word bit inresponse to the monitored CDS of each n-1 bit code word and the openloop DSV control signal, and a combiner adding the DSV modifying codeword bit to each n-1 bit code word to produce a n bit code word having aCDS which produces a DSV of desired value as identified by said openloop DSV control signal.
 19. The tracking system of claim 18 whereinsaid DSV modifying bit generator is a MSB (most significant bit)controller and the DSV modifying bit is the MSB of each n bit code word.20. The tracking system of claim 17 wherein said means for processingdetermines the difference in the signal strength of the low frequencycrosstalk from each of the adjacent tracks to determine the trackingerror in said desired track.
 21. The tracking system of claim 20 whereinsaid differing periodic DSVs of said tracks vary in frequency.
 22. Thetracking system of claim 21 wherein said differing periodic DSVs of saidtracks vary in phase.
 23. The tracking system of claim 22 wherein saidparallel tracks include alternating even and odd tracks, the DSVs ofsaid odd tracks alternating between first and second differingfrequencies.
 24. The tracking system of claim 23 wherein said magneticstorage medium is magnetic tape;said means for storing including arotary drum recording said parallel tracks on said magnetic tape. 25.The tracking system of claim 24 wherein said rotary drum has a pair ofheads mounted thereon and produces a pair of adjacent tracks eachscan;only a first one of each said pair of adjacent tracks having aperiodically varying DSV.
 26. The tracking system of claim 25 whereinthe first ones of adjacent pairs of tracks have periodically varyingDSVs of different frequencies.
 27. The tracking system of claim 23further comprising a low pass filter extracting the low frequencycrosstalk from said reproduction signal; andband pass filter means forfiltering the low frequency crosstalk at said first and second differingfrequencies to recover the pilot signals of the adjacent tracks; saidmeans for comparing the magnitude of pilot signals of the adjacenttracks to produce the tracking error signal.
 28. The tracking system ofclaim 27 further comprising;means for selectively developing a first orsecond DSV signal depending on the track to be recorded; said means forstoring being responsive to said means for selectively developing forstoring a code word having a CDS corresponding to the change in thedeveloped DSV signal associated with each data word.
 29. The trackingsystem of claim 22 wherein said means for storing stores said code wordssuch that alternate tracks, when viewed in a direction transverse to thetracking direction, have DSVs that are 180° out of phase with respect toeach other;said step of comparing developing a difference signal fromthe low frequency crosstalk of the adjacent tracks, said differencesignal having a magnitude and phase indicative of the tracking error insaid desired track.
 30. The tracking system of claim 29 furthercomprising a low pass filter extracting the low frequency crosstalk fromsaid reproduction signal;said means for comparing determining any errorin tracking the desired track from said low pass filtered reproductionsignal.
 31. The tracking system of claim 22 wherein means for storingstores said code words such that alternate tracks, when viewed in adirection transverse to the tracking direction, have DSVs that are 180°out of phase with respect to each other;said means for processingdeveloping a substantially D.C. difference signal from the low frequencycrosstalk of the adjacent tracks, said D.C. difference signal having amagnitude and phase indicative of the tracking error in said desiredtrack.
 32. The tracking system of claim 21 wherein said means forstoring stores the code words in adjacent tracks to form code wordstrings have DSVs which vary with different frequencies.
 33. In a systemwhere data is digitally stored on a magnetic storage medium in paralleltracks, a tracking system comprising:means for storing said data in saidparallel tracks using code words having a periodically varying DSV(digital sum variation), the periodic DSVs of alternate tracks having aphase difference therebetween, said means for storing including,meansfor receiving an open loop DSV (digital sum variation) control signalrepresentative of a desired change in DSV to be produced by each saidcode word, different open loop DSV control signals being produced foradjacent parallel tracks, an encoder receiving said open loop DSVcontrol signal and an M bit data word for storing and developing an Nbit code words having a known CDS (code word digital sum) required toproduce the desired variation in DSV as represented by said DSV controlsignal to make the DSV of said code word string correspond to thedesired DSV, said encoder repeatedly developing N bit code words toproduce a code word string having the a DSV which varies as specified bysaid open loop DSV control signal, and recording means for storing eachof said code words selected in said step of selecting on a said paralleltrack, thereby producing the desired variation in DSV on that saidtrack; said means for storing storing said code word strings on adjacenttracks with differing DSVs as specified by said DSV control signals;means for reading the signals obtained from the desired track to producea reproduction signal, said means for reading further reading lowfrequency crosstalk from adjacent tracks caused by said periodicallyvarying DSV of the data contained in these adjacent tracks; a low passfilter filtering the reproduction signal to recover said low frequencycrosstalk; and a tracking error circuit determining any error intracking the desired track from said low pass filtered reproductionsignal.
 34. The tracking system of claim 33 wherein said tracking errorcircuit determines the difference in the signal strength of the lowfrequency crosstalk from each of the adjacent tracks to determine thetracking error in said desired track.
 35. The tracking system of claim33 wherein said means for storing stores said code words such thatalternate tracks, when viewed in a direction transverse to the trackingdirection, have DSVs that are 180° out of phase with respect to eachother;said tracking error circuit developing a substantially D.C.difference signal from the low frequency crosstalk of the adjacenttracks, said D.C. difference signal having a magnitude and phaseindicative of the tracking error in said desired track.
 36. The trackingsystem of claim 35 wherein said means for storing stores the code wordsin adjacent tracks with DSVs which vary with different frequencies. 37.The tracking system of claim 33 wherein said encoder includes,an n-1 bitencoder developing a code word of n-1 bits from each said data word of mbits, said n-1 bit encoder identifying the CDS of each n-1 bit codeword, a DSV modifying bit generator producing a DSV modifying code wordbit in response to the monitored CDS of each n-1 bit code word and theopen loop DSV control signal, and a combiner adding the DSV modifyingcode word bit to each n-1 bit code word to produce a n bit code wordhaving a CDS which produces a DSV of desired value as identified by saidopen loop DSV control signal.
 38. The tracking system of claim 37wherein said DSV modifying bit generator is a MSB (most significant bit)controller and the DSV modifying bit is the MSB of each n bit code word.39. In a system where data is digitally stored on a magnetic storagemedium in parallel tracks, a method of tracking comprising:storing saiddata in said parallel tracks using code words having a periodicallyvarying DSV (digital sum variation), the periodic DSVs of alternatetracks having a phase difference therebetween, said step of storingincluding the steps of,i) providing data arranged in data words of mbits, <ii) providing an open loop DSV control signal representative of adesired change in DSV to be produced by each said code word, iii)developing a code word of n bits from each said code word of m bits,each said code word of n bits having a CDS (code word digital sum) ofknown value selected in response to said DSV control signal to controlthe DSV of a string of the plural code words to a desired value undercontrol of said DSV control signal, iv) storing each of said code wordsproduced in said step of developing on a said parallel track, therebyproducing the desired variation in DSV on that said track, and v)repeating said substeps i)-v) for adjacent tracks with their associateddifferent DSV signals; reading the signals obtained from the desiredtrack to produce a reproduction signal, said step of reading furtherreading low frequency crosstalk from adjacent tracks caused by saidperiodically varying DSV of the data contained in these adjacent tracks;low pass filtering the reproduction signal to recover said low frequencycrosstalk; and determining any error in tracking the desired track fromsaid low pass filtered reproduction signal.
 40. The method of trackingof claim 39 wherein said step iii) of developing includes the substepsof,developing a code word of n-1 bits from each said data word of mbits, monitoring the CDS of each n-1 bit code word, producing a DSVmodifying code word bit in response to the monitored CDS of each n-1 bitcode word and the open loop DSV control signal, and adding the DSVmodifying code word bit to each n-1 bit code word to produce a n bitcode word having a CDS which produces a DSV of desired value asidentified by said open loop DSV control signal.
 41. The method oftracking of claim 40 wherein said DSV modifying code word bit is the MSB(most significant bit) of each n bit code word.
 42. The method oftracking of claim 39 wherein said step of determining determines thedifference in the signal strength of the low frequency crosstalk fromeach of the adjacent tracks to determine the tracking error in saiddesired track.
 43. The method of tracking of claim 42 wherein said stepof storing stores the code words in adjacent tracks have DSVs which varywith different frequencies.
 44. The method of tracking of claim 39wherein said step of storing stores said code words such that alternatetracks, when viewed in a direction transverse to the tracking direction,have DSVS that are 180° out of phase with respect to each other;saidstep of determining developing a substantially D.C. difference signalfrom the low frequency crosstalk of the adjacent tracks, said D.C.difference signal having a magnitude and phase indicative of the trackerror in said desired track.
 45. In a system where data is digitallystored on a magnetic storage medium in parallel tracks, a trackingsystem comprising:means for storing said data in said parallel tracksusing code words having a periodically varying DSV (digital sumvariation), the periodic DSVs of alternate tracks having a phasedifference therebetween, said means for storing including,means forreceiving an open loop DSV (digital sum variation) control signalrepresentative of a desired change in DSV to be produced by each saidcode word, different open loop DSV control signals being produced foradjacent parallel tracks, an encoder receiving said open loop DSVcontrol signal and an M bit data word for storing and developing an Nbit code words having a known CDS (code word digital sum) required toproduce the desired variation in DSV as represented by said DSV controlsignal to make the DSV of said code word string correspond to thedesired DSV, said encoder repeatedly developing N bit code words toproduce a code word string having the a DSV which varies as specified bysaid open loop DSV control signal, and recording means for storing eachof said code words selected in said step of selecting on a said paralleltrack, thereby producing the desired variation in DSV on that saidtrack; said means for storing storing said code word strings on adjacenttracks with differing DSVs as specified by said DSV control signals;means for reading the signals obtained from the desired track to producea reproduction signal, said means for reading further reading lowfrequency crosstalk from adjacent tracks caused by said periodicallyvarying DSV of the data contained in these adjacent tracks; a low passfilter filtering the reproduction signal to recover said low frequencycrosstalk; and a tracking error circuit determining any error intracking the desired track from said low pass filtered reproductionsignal.
 46. The tracking system of claim 45 wherein said encoderincludes,an n-1 bit encoder developing a code word of n-1 bits from eachsaid data word of m bits, said n-1 bit encoder identifying the CDS ofeach n-1 bit code word, a DSV modifying bit generator producing a DSVmodifying code word bit in response to the monitored CDS of each n-1 bitcode word and the open loop DSV control signal, and a combiner addingthe DSV modifying code word bit to each n-1 bit code word to produce a nbit code word having a CDS which produces a DSV of desired value asidentified by said open loop DSV control signal.
 47. The tracking systemof claim 46 wherein said DSV modifying bit generator is a MSB (mostsignificant bit) controller and the DSV modifying bit is the MSB of eachn bit code word.
 48. The tracking system of claim 45 wherein saidtracking error circuit determines the difference in the signal strengthof the low frequency crosstalk from each of the adjacent tracks todetermine the tracking error in said desired track.
 49. The trackingsystem of claim 48 wherein said means for storing stores the code wordsin adjacent tracks with DSVs which vary with different frequencies. 50.The tracking system of claim 45 wherein said means for storing storessaid code words such that alternate tracks, when viewed in a directiontransverse to the tracking direction, have DSVs that are 180° out ofphase with respect to each other;said tracking error circuit developinga substantially D.C. difference signal from the low frequency crosstalkof the adjacent tracks, said D.C. difference signal having a magnitudeand phase indicative of the tracking error in said desired track.